Mobile multi-hop relay is abbreviated to MMR. Unlike a conventional mobile network, in an MMR network, a relay station (RS) is disposed between an MMR base station (MMR-BS) and mobile stations (MSs). The relay station (RS) relays data packets between the base station (MMR-BS) and mobile stations (MSs) if needed, so that performance of the MMR network can be improved.
FIG. 1 is a view illustrating operations of a relay station.
As shown in FIG. 1, a relay station 200 performs relaying between a base station 100 and a mobile station 300. When the relay station 200 receives a downlink signal from the base station 100 (S101), the relay station 200 transfers the downlink signal to the mobile station 300 (S103). In addition, when the relay station 200 receives an uplink signal from the mobile station 300 (S105), the relay station 200 transfers the uplink signal to the base station 100 (S107).
Due to the relaying of the relay station 200, data throughput can be improved and the cell coverage of a base station 100 can be extended. In addition, shadow areas can be removed, and emergency communication services can be provided. In addition, due to the relay station 200, in-vehicle communication service within a train, a bus, or the like can be provided.
In order to efficiently relay data packets between the base station 100 and the mobile station 300, the relay station 200 needs to transfer various types of control information, such as a various request messages from the mobile station 300 to the base station 100 as well as the information on the time-varying physical channel environment and topology between the relay station 200 and the mobile station 300, to the base station in a timely manner. In addition, the relay station 200 needs to efficiently transfer to the mobile station 300 various types of control information that the base station 100 is to transmit to the mobile station 300.
The control information that the relay station 200 should transmit to the base station 100 and receives from the base station 100 in order to perform the MMR function is described with references to FIGS. 2 and 3.
FIG. 2 is a view illustrating an example of an initial ranging attempt of the mobile station 300 in an MMR network.
In order for the mobile station 300 to register itself to an MMR network, the mobile station 300 transmits a ranging signal to notify the base station 100 of the existence of the mobile station 300 (S201 and S203). When the relay station 200 receives the ranging signal, the relay station 200 transfers the information on the ranging signal to the base station 100 (S205). The base station 100 may or may not receive the ranging signal depending on a position of the mobile station 300. If the base station 100 receives the ranging signal of the mobile station 300, the base station 100 processes the received ranging signal to obtain the ranging information and compares the information with the ranging information received from the relay station 200. If the base station 100 cannot receive the ranging signal of the mobile station 300, the base station 100 identifies the existence of the mobile station 300 based on the ranging information received from the relay station 200. The base station 100 analyzes the collected ranging information to determine whether the mobile station 300 is to communicate with the base station 100 through the relay station 200 or directly. According to the determination, the base station 100 allocates a resource to the mobile station 300 and transmits the control information to the mobile station 300. If the base station 100 directly receives the ranging information from the mobile station 300, the base station 100 waits for the information on the ranging signal that the relay station 200 receives from the mobile station 300 for a predetermined time interval. Therefore, in a case where the relay station 200 exists in a cell, similar to the mobile station 300 that communicates with the base station 100 through the relay station 200, the mobile stations that directly communicate with the base station 100 without the relay station 200 have to experience a longer delay for initial ranging process.
FIG. 3 is a view illustrating a case where a mobile station 300 moves from a coverage area 10A of one relay station 200A to a coverage area 10B of another relay station 200B.
In FIG. 3, two relay stations 200A and 200B are connected to one base station 100. Currently, the mobile station 300 is provided with a service by the relay station 200A (S301 and S303), and the mobile station 300 moves from the coverage area 10A of the relay station 200A to the coverage area 10B of the relay station 200B. When the relay station 200A receives a signal from the mobile station 300 (S301), the relay station 200A measures a reception power of the received signal and transmits information on the reception power to the base station 100 (S305). When the mobile station 300 enters the coverage area 10B of the relay station 200B, the relay station 200B is able to receive the signals from the mobile station 300 (S307) and measures the reception power of the received signal to transmit the information on the reception power to the base station 100 (S309). The base station 100 analyzes the information on the reception intensities received from the relay station 200A and the relay station 200B to det ermine which one of relay paths of the relay station 200A and the relay station 200B is better. If the mobile station 300 is closer to the relay station 200B, the relay station 200B may be determined to be the better relay path. In this case, the base station 100 may switch the relay path to the relay path of the relay station 200B. However, if the relay station 200A and the relay station 200B cannot transmit the information on variation of the reception intensities of the received signals to the base station 100 within a reasonably short time interval, the relay path switching cannot be performed efficiently.
As described with reference to FIGS. 2 and 3, in order to efficiently operate the MMR network, the relay station 200 needs to transmit and receive various types of control information with the base station 100. At this time, if a time delay occurs due to an inefficient transmission of the control information, performance of the MMR network may be degraded.